As fluoropolymers having functional groups, functional group-containing fluoropolymers are known which are used for fluorinated ion exchange membranes, curable fluorinated resin coating materials, etc. However, they are all basically straight chained polymers, and they are obtainable by copolymerization of a fluoroolefin represented by tetrafluoroethylene with a monomer having a functional group.
Further, a polymer containing functional groups and having fluorinated alicyclic structures in its main chain, is also known. As a method for introducing functional groups to the polymer having fluorinated alicyclic structures in its main chain, a method of utilizing terminal groups of a polymer obtained by polymerization, a method of subjecting a polymer to high temperature treatment to oxidize and decompose side chains or terminals of the polymer to form functional groups, or a method of copolymerizing a monomer having a functional group, if necessary, followed by treatment such as hydrolysis to introduce functional groups, is, for example, known (for example, Patent Documents 1, 2, 3 and 4).
The above-mentioned methods are available as methods for introducing functional groups to a polymer having fluorinated alicyclic structures in its main chain. However, the method for introducing functional groups by treating the terminal groups of the polymer, has a drawback that the functional group concentration is low, and no adequate properties of the functional groups can be obtained. Whereas, by the method for introducing functional groups by copolymerizing a monomer having a functional group, there will be a problem such that if the functional group concentration is increased, the mechanical properties tend to decrease due to a decrease of the glass transition temperature (Tg).
Patent Document 1: JP-A-4-189880
Patent Document 2: JP-A-4-226177
Patent Document 3: JP-A-6-220232
Patent Document 4: WO02/064648